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A234007 Free polyominoes with 4n squares, having 90 degree rotational symmetry about a square corner, but not having reflectional symmetry on axis that coincides with edges. 5
0, 1, 2, 9, 30, 110, 387, 1419, 5185, 19225, 71634, 269250, 1017260 (list; graph; refs; listen; history; text; internal format)



The number of free polyominoes of size 4n that have 90 degree rotational symmetry about a point that coincides with the corner of a square, and that have not at the same time reflectional symmetry on a horizontal or vertical axis that coincides with the edges of some of the squares. Note that for polyominoes which have a hole in the center, the center of rotation will be the corner of a square within the hole, rather than being the corner of a square of the polyomino itself. The sequence is defined for 4n rather than n as polyominoes of size not multiple of 4 cannot have the required symmetry.


Table of n, a(n) for n=1..13.


Cf. A000105, A001933, A234006, A234008, A234009, A234010.

Sequence in context: A289901 A261330 A101604 * A203365 A181954 A318101

Adjacent sequences:  A234004 A234005 A234006 * A234008 A234009 A234010




John Mason, Dec 18 2013


a(8)-a(13) from Sean A. Irvine, Jul 04 2019



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Last modified November 14 01:24 EST 2019. Contains 329108 sequences. (Running on oeis4.)